1. Field of the Invention
The present invention relates to a solenoid-operated valve controller for controlling a solenoid-operated valve having a plurality of solenoid coils.
2. Description of the Related Art
There has heretofore been known a double-solenoid-operated valve having two electromagnetically operated pilot valves that are actuated by solenoid mechanisms. This known type of double-solenoid-operated valve has a main spool for changing the direction of a flow of a main fluid, with two pistons disposed respectively on opposite axial ends of the main spool. The two solenoid mechanisms are alternately turned on and off to cause a pilot fluid to act alternately on the two pistons, thereby to shift the main spool.
Japanese Laid-Open Utility Model Publication No. 5-96654, for example, discloses a conventional double-solenoid-operated valve having two pistons having different diameters and disposed respectively on opposite axial ends of a main spool. While a pilot fluid pressure is applied to the smaller-diameter piston by a manual operation unit, one of the pilot valves is turned on or off to supply the pilot fluid to or discharge the pilot fluid from the larger-diameter piston, to thereby shift the main spool in the same manner as a single-solenoid-operated valve.
Another conventional double-solenoid-operated valve having two electromagnetically operated pilot valves, as disclosed in Japanese Laid-Open Patent Publication No. 8-145225, can be used as a single-solenoid-operated valve having a single pilot valve. When the disclosed valve is used as a double-solenoid-operated valve, the main spool is prevented from being shifted, even if the two pilot valves are simultaneously turned on in error.
There have heretofore been proposed power-saving techniques for actuating solenoid-operated valves. For example, Japanese Laid-Open Patent Publication No. 3-213782 reveals a solenoid-operated valve controller for applying a rated voltage to the solenoid coil of a solenoid-operated valve, for a predetermined period based on a drive command signal, and then applying a holding voltage lower than the rated voltage to the solenoid coil of the solenoid-operated valve, for a remaining period of the valve activation interval, thereby to actuate the solenoid-operated valve while achieving a power savings.
U.S. Pat. No. 6,164,323 discloses a solenoid valve control system, wherein a microprocessor operates according to control signals, so as to apply power at a 100% duty cycle to the solenoid coil of the valve for a predetermined period of time, to thereby move a movable member inside the solenoid coil, and then apply power at a reduced duty cycle to the solenoid coil, to thereby keep the valve activated at a reduced level of power consumption for a remaining period of the valve activation interval, thereby holding the movable member in position inside the solenoid coil.
Efforts have been made to reduce the size of double-solenoid-operated valves, and also to make structural changes for placing the two solenoid coils on one side. Because of such efforts, the space made available for installing control circuits for the two solenoid coils is reduced, so that individual control circuits for the respective solenoid coils cannot be installed within the available space.
The spool of the solenoid-operated valve, which is operated at a level of reduced power consumption, is held in place under weak forces. When a strong shock is applied to the solenoid-operated valve, the movable member tends to be shifted out of position, changing the fluid passages provided in the solenoid-operated valve. As a result, a cylinder that is actuated by fluid flowing through the fluid passages may operate unexpectedly.
The above drawback can be avoided by monitoring the state of the movable member of the solenoid-operated valve using a sensor. However, a solenoid-operated valve incorporating such a sensor and its associated circuitry becomes complex in structure and expensive to manufacture.